The Welsh All Blacks powered past Newbridge 22-5 in sodden conditions to take the No 1 spot, although the Black and Ambers have two games in hand.
Wales international Adrian Durstan's stunning burst from fullback triggered the game's opening try, finished off by centre John Leyshon, who is enjoying a profitable season in this division.
Visiting fly-half Matthew Jones put the match beyond doubt with a superb solo 70-metre try midway through the second half, and the promising youngster ended the match with a vital 12 points.
Elsewhere, Aberavon got their up-and-down season back on track with a hard-fought 22-15 victory at Cross Keys. A brace of tries to centre David Hawkins helped the Wizards overturn a 7-8 deficit at Pandy Park.
In another tight match, Carmarthen Quins shifted up a gear in the second half to turn Bedwas' 15-5 lead into a 15-20 loss, while Llandovery's Ricky Williams kicked 10 points in his side's 20-13 victory over Caerphilly.
Ebbw Vale climbed off the bottom of the League table with a thrilling 22-20 win over Bridgend, which consigns Cardiff to last place in the division.
In the final fourth-round tie in the Konica Minolta Cup, Premier Division side Swansea returned from Fourth Division Ynysddu with a simple
Matthew Brayley scored three of his side's 13 tries in the match, and the All Whites are home to Nantyffllon in the fifth round.
Konica Minolta Cup - Round Four: Ynysddu 0 Swansea 79.
Premier Division: Bedwas 15 Carmarthen Quins 20, Cross Keys 15 Aberavon 22, Ebbw Vale 22 Bridgend 20, Llandovery 20 Caerphilly 13, Newbridge 5 Neath 22.